MDEV-17256 Decimal field multiplication bug.bb-5.5-hf

We should clear trailing zeroes in frac part. Otherwise
that tail is growing quickly and forces unnecessary truncating of
arguments.

1 files changed, 19 insertions, 16 deletions

diff --git a/strings/decimal.c b/strings/decimal.c
index 3d90a58ea8a..05546aa77a3 100644
--- a/strings/decimal.c
+++ b/strings/decimal.c
@@ -2077,26 +2077,21 @@ int decimal_mul(const decimal_t *from1, const decimal_t *from2, decimal_t *to)
     }
   }
 
-  /* Now we have to check for -0.000 case */
-  if (to->sign)
+  /* Remove trailing zero words in frac part */
+  frac0= ROUND_UP(to->frac);
+
+  if (frac0 > 0 && to->buf[intg0 + frac0 - 1] == 0)
   {
-    dec1 *buf= to->buf;
-    dec1 *end= to->buf + intg0 + frac0;
-    DBUG_ASSERT(buf != end);
-    for (;;)
+    do
     {
-      if (*buf)
-        break;
-      if (++buf == end)
-      {
-        /* We got decimal zero */
-        decimal_make_zero(to);
-        break;
-      }
-    }
+      frac0--;
+    } while (frac0 > 0 && to->buf[intg0 + frac0 - 1] == 0);
+    to->frac= DIG_PER_DEC1 * frac0;
   }
+
+  /* Remove heading zero words in intg part */
   buf1= to->buf;
-  d_to_move= intg0 + ROUND_UP(to->frac);
+  d_to_move= intg0 + frac0;
   while (!*buf1 && (to->intg > DIG_PER_DEC1))
   {
     buf1++;
@@ -2109,6 +2104,14 @@ int decimal_mul(const decimal_t *from1, const decimal_t *from2, decimal_t *to)
     for (; d_to_move--; cur_d++, buf1++)
       *cur_d= *buf1;
   }
+
+  /* Now we have to check for -0.000 case */
+  if (to->sign && to->frac == 0 && to->buf[0] == 0)
+  {
+    DBUG_ASSERT(to->intg <= DIG_PER_DEC1);
+    /* We got decimal zero */
+    decimal_make_zero(to);
+  }
   return error;
 }